Sites that use a device-width viewport but don't have enough height to fill the view...

Sites that use a device-width viewport but don't have enough height to fill the view are scaled up
https://bugs.webkit.org/show_bug.cgi?id=142664
<rdar://problem/18859470>

Reviewed by Benjamin Poulain.

* page/ViewportConfiguration.cpp:
(WebCore::ViewportConfiguration::shouldIgnoreHorizontalScalingConstraints):
(WebCore::ViewportConfiguration::shouldIgnoreVerticalScalingConstraints):
(WebCore::ViewportConfiguration::shouldIgnoreScalingConstraints):
Split shouldIgnoreScalingConstraints into one for each dimension.

(WebCore::ViewportConfiguration::initialScale):
(WebCore::ViewportConfiguration::minimumScale):
Don't force the initial and minimum scales to cover the whole view if the
page claims to want to lay out to device width but then lays out too big.
This will allow pages that misbehave in this way to scale down further
than they previously could, but will result in a region of empty background
color being exposed at the initial/minimum scale.

(WebCore::ViewportConfiguration::description):
Update the logging to show each dimension separately.

* page/ViewportConfiguration.h:

* UIProcess/ios/WKScrollView.mm:
(-[WKScrollView _rubberBandOffsetForOffset:maxOffset:minOffset:range:outside:]):
Now that the WKContentView can (without pinching) be smaller than the unobscured
region of the WKWebView, we need to take that into account when deciding where
to retarget scrolling.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@181488 268f45cc-cd09-0410-ab3c-d52691b4dbfc